1. Field of the Invention
The present invention generally relates to telecommunications switching systems and more particularly, to a code division multiplexed switching system which uses multiple access codes to encode the data. In this system, path selection is performed, in part, by encoding and decoding systems associated with each node in the switch.
2. Description of the Prior Art
In recent years the computational power of data processing systems has increased very rapidly. In particular, there has been a marked increase in the use of multiple processing elements operating concurrently under control of a single program--or a suite of related programs--to solve a single problem. These processing elements may be located in close proximity, as in a tightly coupled processing environment, or they may be at distant locations, linked to each other through a complex data processing network. In systems of this type, communication of both data and control information among the processors is an important factor in determining the efficiency of the multiple processor system.
Traditionally, this interprocessor communication has been implemented by a switching system which is coupled to each processor and which includes a controller for routing data among the multiple processing elements. A switching system of this type, operating in a processing network that includes high performance processors, desirably includes a signal transmission medium having a wide bandwidth and a controller which can route data among the processors connected to the system quickly and in a manner that avoids conflicts among the processors for access to the available communications channels.
A fiber optic transmission medium has a bandwidth suitable for such a high performance processing network. However, the increase in bandwidth afforded by the use of a fiber optic transmission medium should be matched by a comparable increase in the processing speed of the switch controller. Otherwise, the overall efficiency of the switch will be less than is desirable for a high performance processing system. The coupling of switch controllers in order to increase the efficiency of the switching system is, however, a much more difficult task than the relatively simple coupling of transmission lines. In other words, the parallel processing of the switch routing commands is not as simple as the parallel transmission of data. Thus, the switch controller is likely to become a bottleneck in future high-speed switching facilities.
One way around this problem is to transfer some of the real-time control functions from the controller to other components of the switching system. In the limit, this approach would produce a self-routing switching system, that is to say, one without a controller. In a switching system of this type, message routing would be inherent in the design of the transmission components. A self-routing system of this type may be realized using code division multiple access (CDMA) techniques, as set forth below.
In the prior art, U.S. Pat. No. 3,715,508 to Blasbalg describes a switching circuit which uses a plurality of pseudo-random, mutually orthogonal code sequences to encode a plurality of messages. The encoded messages are linearly summed to generate a signal for transmission. The signals are decoded by a plurality of receivers, each of which arithmetically processes the summed message signal with a respective regenerated code. These codes are pseudo-random sequences, identical to those used encode the data. A final step in the decoding operation is to integrate the processed signals produced by each of the receivers. Since the codes are mutually orthogonal, each receiver will recover only one message from the summed message signal.
U.S. Pat. No. 4,475,186 to Gutleber describes a switching system which uses a plurality of pseudo-random code sequences to encode a plurality of messages. Each of these code sequences autocorrelates to a lobeless impulse function and, at the peak of the autocorrelation function, exibits zero crosscorrelation with each other code sequence of the plurality of code sequences. This property makes the code sequences mutually orthogonal. This switching system automatically directs a message applied to a specific input line to a selected output line which is matched to the code used on the specific input line.